Ethernet over Unshielded Twisted Pair (UTP) cables based on the 10 Base-T standard (as described in sections 13 and 14 of IEEE Standard 802.3i-1990--that is a supplement to ISO/IEC 8802-3:1990, Product Number SH16337 available from IEEE Service Center, 445 Hoes Lane, P.O. Box 1331, Piscataway, N.J., USA 08855-1331, and that is incorporated herein in its entirety), using hub cards (sometimes referred to as "concentrators" or "repeaters") in the center of a star-wired configuration is popular in modern offices. Use of UTP cables that can also be used in telephone systems provides flexibility to moves, changes and additions, without rewiring the modern office.
One example of prior art hub cards are ISA hub cards 101-103 (FIG. 1A) that contain a predetermined number of ports, such as Twisted Pair (TP) ports J4 (FIG. 1A), that support an ethernet with eight 10 Base-T stations, for example, personal computers (PCs).
ISA hub cards 101-103 of FIG. 1A are 10 Base-T Ethernet repeater cards, such as "ISA-HUB.TM.-KT" available from Advanced Micro Devices, Inc. (AMD.TM.), One AMD Place, P.O. Box 3453, Sunnyvale, Calif. 94086, and described in ISA-HUB.TM. Users' Manual (also available from AMD.TM.), that is incorporated by reference herein in its entirety.
An ISA hub card, such as card 101, supports the physical topology of an Ethernet network, allowing two or more 10 Base-T stations that are connected to connectors J4 to communicate with each other. When data is received on a single port of connector J4, ISA hub card 101 retransmits the received data to all other ports of connector J4, performing signal retiming and amplitude restoration. When data appears simultaneously on more than one port, ISA hub card 101 transmits a collision signal to all ports of connector J4, including ports of the transmitting and receiving 10 Base-T stations.
ISA hub cards 101-103 can be supported by a single system board 110 to take advantage of shared costs, for example, of the power suppply. Use of a single system board 110 offers easy expansion by allowing installation of additional hub cards (not shown). Although only three ISA hub cards are illustrated in FIG. 1A, up to eight ISA hub cards can be mounted on system board 110. Use of a single system board 110 also allows use of redundant power supplies, support for multiple LAN segments, support for different media access protocols, such as token ring and different media types such as UTP, coaxial cable and fiber optics.
An expansion interface comprising connectors J1 and J2 (FIG. 1A) in each ISA hub card 101-103 allows a number of ISA hub cards 101-103 to act in concert as a single aggregate ISA hub, thereby providing a single ethernet network for an office that contains a larger number of PCs (e.g. 24 PCs) than the number of ports (e.g. 8 ports) on a single ISA hub card. In such a case, a connector, e.g. connector J1 of an ISA hub card is connected to a corresponding connector, e.g. connector J1, of another ISA hub card. Connection of multiple ISA hub cards is described in for example, "IEEE 802.3 Repeater, Technical Manual" available from AMD.TM. (above), and that is incorporated by reference herein in its entirety. ISA hub cards 101-103 are interconnected by conventional cables, such as cable 120 (FIG. 1B) that has straight through, e.g. one-to-one wiring 131-135 between a left connector 140 having terminals 141-145 and a right connector 150 having terminals 151-155.
Any of ISA hub cards 101-103 can be configured to perform a master function by placing a single jumper in the "M" position as described in the ISA-HUB.TM. User's Manual referenced above. All ISA hub cards in an aggregate ISA hub, other than a master ISA hub card, are slaves that are assigned unique identities by placing a single jumper (e.g. jumper JP1 in FIG. 1A) at a unique position other than the M position as described in the ISA-HUB.TM. User's Manual (above).
In a prior art ethernet, the master ISA hub card is also responsible for reset synchronization and for centralized arbitration. Centralized arbitration is performed by a programmable array logic (PAL.TM.) device 115 of the master ISA hub card. Although a PAL.TM. device is included in every ISA hub card, only the PAL.TM. device in a master ISA hub card is enabled.
The master ISA hub card's PAL.TM. device 115 (also called master arbitration PAL.TM. device) performs centralized arbitration by monitoring request signals on a number of request lines of cable 120. Each request signal originates from one of ISA hub cards 101-103 as follows. The PAL.TM. device of a ISA hub card that receives a packet from an ethernet node drives a request signal active and waits for an acknowledge signal to go active before transmitting the received packet to other ISA hub cards e.g. on cable 120.
Master arbitration PAL.TM. device 115 generates a collision signal that is transmitted on a collision line to all ISA hub cards 101-103 when more than one request line is active simultaneously. If only one request line has an active request signal, master arbitration PAL.TM. device 115 generates an acknowledge signal that is also transmitted to all ISA hub cards 101-103. Only the ISA hub card that generated the active request signal responds to the active acknowledge signal and transmits a packet e.g. on cable 120. All other ISA hub cards wait to receive the packet in response to the active acknowledge signal.
The principles of centralized arbitration are explained in detail in the prior art, for example, in section 5.5.2 at page 5-9 of "IEEE 802.3 Repeater, Technical Manual" that was incorporated by reference above. Equations for implementing such a master arbitration PAL.TM. device are also well known, for example, as listed in section 5.5.4 at page 5-10 of "IEEE 802.3 Repeater, Technical Manual" (above).
Centralized arbitration has several drawbacks. For example, centralized arbitration requires that a slave ISA hub card 101-103 wait for the time required for a request signal to travel the expansion cable distance (e.g. distance D in FIG. 1A) between the slave ISA hub card and master ISA hub card and the time required for an acknowledge signal to travel back the expansion cable distance from the master ISA hub card, which wait imposes a limitation on the speed of the network (such as an ethernet). In one prior art ethernet, a slave ISA hub card waits for a travel time of 100 nanoseconds, which wait limits the prior art ethernet to a speed of 10 megahertz. Also, a malfunction in the master arbitration PAL.TM. device can cause unpredicted and improper operation of the aggregate hub.